The rule for countable ingredient pluralization appears to be:
If more than one countable ingredient is necessary to fill the required amount, then the ingredient is pluralized.
- 2 cups watermelon
- 2 watermelons
- 2 barrels watermelons
- 2 tsps egg yolk
- 1 cup egg yolks
When writing a cookbook, what determines whether a countable ingredient should be pluralized (in the ingredient list)?